1. Field of the Invention
The present invention relates to a light source system capable of effectively dissipating heat, and more particularly, to a light source system capable of improving light degradation, and adjusting output luminance and chrominance of light.
2. Description of the Prior Art
In daily life, people need to change luminance and chrominance of light for different environments. For example, soft light is for dining, and bright but not harsh light is for reading. Therefore, for conveniently controlling light, different methods are provided in the prior art, such that users can change the luminance and chrominance of light emitted by a light-emitting device, such as a light emitting diode, via a switch. Since the luminance and chrominance of light emitted by a light-emitting device are related to amplitude, duty cycle, or total power of an input power, the above method alters amplitude, duty cycle or total power of the input power, to adjust the luminance and chrominance of light. A method of altering the duty cycle is often realized by angular modulation, such as pulse width modulation (PWM).
Please refer to FIG. 1, which is a schematic diagram of a conventional light source system 10. The light source system 10 includes a light-emitting device 100, a switch device 102 and a pulse width modulation device 104. The light-emitting device 100 can be a light emitting diode, and is utilized for generating a light source according to received power. The switch device 102 can be an on-off switch, and is utilized for receiving control signals triggered by a user and transmitting the control signals to the pulse width modulation device 104. The pulse width modulation device 104 is utilized for transforming an input signal VIN into an output signal VOUT according to signals provided by the switch device 102, and transmitting the output signal VOUT to the light-emitting device 100 to emit light. When the user needs to control luminance and chrominance of light emitted by the light-emitting device 100, the user can utilize the switch device 102 to adjust pulse width of the output signal VOUT, i.e. T1, such that the light-emitting device 100 can emit light according to requirements.
Via the pulse width modulation device 104, the user can adjust luminance and chrominance of the light generated by the light source system 10. However, a circuitry of the pulse width modulation device 104 is very complicated, resulting in high production cost which limits its applications. Besides, utilizing the waveform generated by the pulse width modulation device 104 would still have the following problems:
First is light degradation, which means that luminance of the light emitting diode degrades as operating time increases under the same driving power, is most obvious when the light emitting diode is initially activated. In other words, luminance degradation is most obvious when a light emitting diode is turned on at the first time. Therefore, although the light emitting diode has long life time, the light degradation and deterioration of fluorescent powder and packaging materials would reduce luminous flux after long-term operation. When the luminous flux decreases to a specific degree, the effective life of the light emitting diode is over, i.e. can not meet requirements of illumination or backlight applications.
Second is heating of a light emitting diode chip. Though volume of a packaged light emitting diode is not small, surface area of a light emitting diode chip in some products is often less than 1 mm2. In such a situation, the operating current density is great, such that the diode is significantly heated. If the heat can not be dissipated, the chip will be damaged easily. In addition, in order to meet requirements of illumination, a plurality of light emitting diodes are cascaded, causing significant temperature rising after long-term operation. In order to dissipate heat effectively, extra heat-dissipation areas need to be added, resulting in more complexity of external structures design.
Therefore, utilizing PWM in a light dimmer would still face light degradation and overheating. Thus, there is a need of improvement.